This invention relates to an internal combustion engine and particularly to an improved induction system for an internal combustion engine that facilitates its use as the power plant of an outboard motor or other marine propulsion unit.
It is well known that internal combustion engines are used as a power source in many applications. Also, in many of these applications it is desirable to maintain the engine and its auxiliaries such as the induction system quite compact in nature. One particular application for internal combustion engines where this is true is in outboard motors. In an outboard motor, the engine forms a portion of the power head and is contained within a protection cowling. It is desirable to maintain the power head relatively compact and this gives rise to a number of problems in the design of the engine and its auxiliaries.
These problems are particularly true when the powering internal combustion engine is of the four-cycle type and includes an overhead valve mechanism. With such engines, the induction system which provides at least an air charge to the combustion chambers generally extends transversely outwardly from one side of the cylinder head. This has a tendency to make the engine very bulky and requires a large protective cowling.
In order to avoid these problems, it would be possible to have the induction system extend from the cylinder head down along one side of the cylinder block to maintain a more compact nature. Normally the induction system for outboard motors includes a plenum chamber that serves the function of tuning the intake passages for good engine induction efficiency and also for silencing the intake air. Therefore, it is generally desirable to maintain a relatively large volume for the plenum chamber. However, when the plenum chamber extends along the side of the cylinder block, then enlargement of its volume presents problems and can again cause the engine to become bulky in a transverse direction and require large protection cowlings. Also, this positioning for the plenum chamber somewhat shortens the length of the intake passages that extend from the plenum chamber to the cylinder head intake port and makes tuning of the induction system, particularly for good mid-range performance, very difficult.
It is, therefore, a principle object of this invention to provide an improved internal combustion engine and induction system therefor.
It is a further object of this invention to provide an improved and compact induction system for an internal combustion engine that facilitates its use in an outboard motor and which permits tuning of the induction system.
From the foregoing description it should be apparent that it is desirable to position the induction system for an engine along one side of the cylinder block, particularly when utilized in conjunction with an outboard motor. However, this positioning with conventional cylinder head intake porting requires an intake manifold that snakes around the cylinder head and back toward the cylinder block. Such intake manifolds are difficult to fabricate, add to the expense of the engine and also make the engine more bulky.
It is, therefore, a still further object of this invention to provide an improved cylinder head intake passage arrangement.
It is a further object of this invention to provide an improved cylinder head intake passage arrangement for an engine that facilitates its use with outboard motors.